It has been customary to employ air to cool hot pellets discharged from a rotary kiln or the like within a reduced atmosphere or to indirectly air cool the same within a sealed container when it is necessary to avoid oxidation of the pellets. However, in either of the air cooling processes referred to above, the cooling efficiency is not satisfactory and oxidation also may be encountered during the cooling process. Further, a large apparatus is required for air cooling due to its low efficiency and, accordingly, it requires a large installation area and consumes much power thereby making it uneconomical.
Thus, it has also been proposed to apply a water spray as cooling medium for the hot pellets. Such a water cooling apparatus generates a large volume of vapor which makes it impracticable to dispose the apparatus coupled in series with a rotary kiln or the like, since the treatment of such volume of vapor is difficult. Therefore, the pellets are likely to be oxidized in the course of being cooled. Further, these days, if such vapor is exhausted into the open air through a chimney of the plant, it becomes white smoke likely to cause complaints about the environmental pollution.
Also, if it is attempted to connect the water cooling apparatus with the kiln or the like, the generated vapor may get into the inside of the kiln whereby the firebricks of the kiln may be degraded or damaged and the life of the kiln is shortened.